In liquid crystal display devices, a plurality of pixel circuits are arrayed along an X-direction (, which may be referred to as row direction) and a Y-direction (, which may be referred to as a column direction). The X-direction crosses the Y-direction. For example, a plurality of gate lines parallel to the X-direction are arranged at certain intervals along the Y-direction. Further, a plurality of source lines parallel to the Y-direction are arranged at certain intervals along the X-direction. The pixel circuits are located near intersections of the gate lines and the source lines, respectively.
In some liquid crystal display devices, the pixel circuits each comprise a digital memory. With the pixel circuits with digital memories, when, for example, a static image is displayed in the entire display area of the device for a long time, pixel signals need not be rewritten to all the source lines. Thus, power consumption can be reduced in the device. In addition, when a static image is displayed in a part of the display area, and moving images are displayed in the remaining part, there is no need to frequently apply voltage to all the source lines. In this case, too, the power consumption of the display device can be reduced because the pixel signal for moving images should be supplied only to source lines of the rest of the display area.